Contents - Faperta

224 Biotechnological Approaches for Pest Management and Ecological Sustainability
Vegetative Insecticidal Proteins
A supernatant of vegetative Bacillus cereus (Frankland and Frankland) culture has two
compounds; VIP 1 and VIP 2, which have been shown to possess toxic effects toward
insects (Estruch et al., 1997). VIP 3 is highly toxic to Agrotis and Spodoptera (Estruch et al.,
1996). The activity of these proteins is similar to d-endotoxins of Bt. The acute toxicity of
vegetative insecticidal proteins is in the same range as that of the d-endotoxins from Bt.
They induce gut paralysis, followed by complete lysis of the gut epithelium cells, resulting
in larval mortality. The vip3Aa14 gene from B. thuringiensis tolworthi was expressed in
Escherichia coli Escherich using expression vector pET29a (Bhalla et al., 2005). The expressed
Vip3Aa14 protein was found in cytosolic supernatant as well as pellet fraction, but the
protein was more abundant in the cytosolic supernatant fraction. Both full-length and
truncated (devoid of signal sequence) Vips were highly toxic to the larvae of S. litura and
P. xylostella. Rang et al. (2005) produced the Vip3Ba1 protein in E. coli and tested against the
European corn borer, O. nubilalis and the diamondback moth P. xylostella. The expressed
protein resulted in signifi cant growth delays, but had no larvicidal effect, indicating that
its host range might be different than that of Vip3A proteins. Several transgenic events of
cotton and corn are under fi eld testing to be deployed for pest management in the near
future (Christou et al., 2006).
Toxin Proteins from Photorhabdus luminescens
The tcdA gene of Photorhabdus luminescens (Thomas and Poinar) Boemare et al. encoding a
283 kDa protein (toxin A), which is highly toxic to insects, has been expressed in Arabidopsis
thaliana (L.) Heyn. The transgenic plants expressed the protein at 700 ng mg 1 of extractable
protein, and were highly toxic to tobacco hornworm, M. sexta (D. Liu et al., 2003). Toxin A
isolated from the transgenic plants also inhibited the growth of the Southern corn rootworm,
D. undecimpunctata howardi. Addition of 5¢- and 3¢-untranslated regions of a tobacco
osmotin gene (osm) increased toxin A production 10-fold and recovery of insect-resistant
lines 12-fold. In the best line, high expression of toxin A and insect resistance were maintained
for at least fi ve generations. The intact tcdA mRNA represented the largest effective
transgenic transcript produced in plants to date.
Secondary Plant Metabolites
Many secondary plant metabolites, such as alkaloids, steroids, foliar phenolic esters, terpenoids,
saponins, fl avonoids, and nonprotein amino acids, act as potent protective chemicals.
Some of the secondary plant metabolites are produced in response to insect feeding
(H.C. Sharma and Agarwal, 1983; Ebel, 1986; H.C. Sharma and Norris, 1991). Systemically
induced responses are modifi ed through synthesis and action of jasmonic acid via its lipid
precursor, for example, linoleic acid in tomato. Exogenous application of jasmonate induces
the production of proteinase inhibitors. Xu et al. (1993) observed enhanced resistance in
rice by wounding methyl jasmonate and abscisic acid in transgenic plants. Effective manipulation
of secondary metabolites by introduction (or elimination by antisense RNA technology)
of enzyme encoding sequences is quite diffi cult (Hallahan et al., 1992; McCaskill
and Croteau, 1998), and increased production of many of these chemicals may impose a
measurable cost in productivity potential of crop plants (Vrieling, van Wijk, and Swa, 1991).
Such cost is not involved in natural protection mechanisms based on protective proteins
(Brown, 1988). Expression of relatively large amounts of a foreign protein such as cowpea